1. Field of the Invention
The invention generally relates to a dielectric ceramic composition. More particularly, the invention relates to a dielectric ceramic composition that comprises BaTiO3 as the main component and one or more subcomponents to improve the capacitor-temperature characteristic and sinterability of the main component BaTiO3 so that the dielectric ceramic composition may have broader applications and higher stability.
2. Description of the Prior Art
Diamond film and diamond-like carbon exhibit predominantly high visible and infrared (IR) transmission, high mechanical strength, high electric resistance, and resistance to corrosive gas or other medium. Consequently, they can be used as highly protective materials and anti-reflective coatings. Owing to the energy crisis, research in thin-film solar cells has attracted much attention. Among materials useful in solar cells, silicon crystals have unique semiconducting characteristics and therefore can be used in semiconducting elements and solar cells. On the other hand, although diamond materials have atomic structure similar to that of silicon crystals, they are inherently an insulating material. Accordingly, a number of researchers have attempted to change the electrical property of diamond material to make it semiconducting or conducting by means of doping techniques so as to favor the application and development of diamond materials. Among those attempts, changing the electric resistance of diamond film or diamond-like carbon (DLC) film by means of doping could make it possible for diamond film or diamond-like carbon film to be applied in semiconductor or electrical elements. Methods for lowering the electric resistance of diamond film or diamond-like carbon included doping of hydrogen phosphide or diborane, blending to form metal film, nitrogen infiltration during film deposition and the like.
As technology advances, material or composition plays an important role in various types of components. Because the X7R multilayer ceramic capacitor has a stable temperature coefficient of capacitance (ΔC/C≦±15% in the temperature range from −55 to 125 degree C.), it has been widely used in miniaturized electronic components that operate in a large temperature variation range. In recent years, multilayer ceramic capacitors have been used in the electronic components of automobile, such as ECU (engine electronic control unit), ABS (antilock brake system) module and PGMFI. These electronic components often have to operate in a large temperature variation range, and the X7R multilayer ceramic capacitor is not able to meet this demand. For the sake of safety, the EIA (Electronic Industries Association) has stipulated the standard for X8R characteristic (AC/C≦±15% in the temperature range from −55 to 150 degree C.) and ceramic materials or compositions meeting this standard have attracted a lot of attention.
In terms of the internal electrodes in the production process of the multilayer ceramic capacitor, the production process may be categorized into two types: precious metal process and inexpensive metal process. In the precious metal process, an alloy of silver and palladium has often been used as the internal electrodes. Therefore, the production cost is high. On the other hand, in the inexpensive metal process, an alloy of copper and nickel has often been used as the internal electrodes. Because copper and nickel are subject to oxidation, sintering has to be performed in a reducing atmosphere. In addition, the dielectric characteristics of many types of dielectric compositions would change after they undergo sintering in a reducing atmosphere.
In the prior art, dielectric compositions comprising Bi2O3, PbO and TiO2 are often used for ceramic capacitors that require a stable temperature coefficient of capacitance. Because these dielectric compositions contain lead and the EU has restrictions against the use of lead, the aim of the present invention is to come up with a dielectric ceramic composition that satisfies the X8R characteristic of the EIA standard and has a high dielectric constant.
At a Tc (Curie temperature), the crystalline structure would change from a cubic structure to a tetragonal structure and a dielectric peak would occur. Therefore, these two factors limit the applications of the compositions of the prior art. Because BaTiO3 has a high dielectric constant, it is often used in passive components; in addition, composition with a high dielectric constant would enable a component to be more compact and lighter. Because the capacitor-temperature characteristic of BaTiO3 needs to be improved, the compositions of the prior art needs to be modified.
In addition, in the development of the X8R multilayer ceramic capacitors, BaTiO3 has been used as the main component and one or more subcomponents (such as modifier, crystalline structure inhibitor and sintering auxiliary reagent) have been added to improve the capacitor-temperature characteristic and the sinterability.
To improve the capacitor-temperature characteristic, subcomponents are added; such addition causes chemical inhomogeneity and the formation of core-shell structure. The molecules of the pure BaTiO3 form the core in a cubic structure that is paraelectric. The mixture of BaTiO3 and the subcomponents form the shell in a tetragonal structure that is ferroelectric. Therefore, by changing the mole percentages of the subcomponents, one can shift Tc, and improve capacitor-temperature characteristic to satisfy the X8R characteristic.
There have been several US patents relating to the subject.
In U.S. Pat. No. 6,764,976, a ceramic composition is disclosed. 100 moles of BaTiO3 is used as the main component and the subcomponents include (1) 0 to 0.1 mole of the oxides of Mg, Ca, Ba and Sr (2) 1.0 to 7.0 moles of the oxides of Y, Dy, Ho and Er (3) 0 to 5.0 moles of CaZrO3 (4) 2.0 to 10.0 moles of the silicic acids of Ba, Ca, Sr, Li and B (5) 0 to 0.5 mole of the oxides of Mn and Cr (6) 0.01 to 0.5 mole of the oxides of V, Mo and W. Such ceramic composition can satisfy the X8R characteristic of the EIA standard.
In U.S. Pat. No. 6,809,052, another ceramic composition is disclosed. 100 moles of BaTiO3 is used as the main component and the subcomponents include (1) 0.1 to 5.0 moles of the oxides of Mg, Ca, Ba and Sr (2) 2.0 to 10.0 moles of SiO2 (3) 0.8 to 1.2 moles of (Ba, Ca)xSiO2+x as the sintering auxiliary reagent (4) 0.5 to 0.7 mole of the oxides of V, Mo and W (5) 0.1 to 10.0 moles of R1 (its “CN” is 9 and the ion radius is less than 108 pm) and 0.1 to 10.0 moles of R2 (its “CN” is 9 and the ion radius is in the range from 108 pm to 113 pm) (the total quantity of R1 and R2 is less than 10.0 moles) (6) 0 to 0.5 mole of the oxides of Mn and Cr. Such ceramic composition can satisfy the X8R characteristic of the EIA standard.
In U.S. Pat. No. 6,999,302, another ceramic composition is disclosed. 100 moles of BaTiO3 is used as the main component and the subcomponents include (1) 0.1 to 3.0 moles of the oxides of Mg, Ca, Ba and Sr (2) 2.0 to 10.0 moles of SiO2 (3) 0.01 to 0.5 mole of the oxides of W, V and Mo (4) 0.5 to 7.0 moles of R1 (Sc, Er, Tm, Yb and Lu) (5) 0 to 5.0 moles of CaZrO3 (6) 2.0 to 8.0 moles of R2 (Y, Dy, Ho, Tb, Gd and Eu). Such ceramic composition can satisfy the X8R characteristic of the EIA standard.
In U.S. Pat. No. 7,061,748, another ceramic composition is disclosed. 100 moles of BaTiO3 is used as the main component and the subcomponents include (1) 0.1 to 3.0 moles of the oxides of Mg, Ca, Ba and Sr (2) 2.0 to 10.0 moles of SiO2 (3) 0.01 to 0.5 mole of the oxides of W, V and Mo (4) 0.5 to 7.0 moles of R1 (Sc, Er, Tm, Yb and Lu) (5) 0 to 5.0 moles of CaZrO3 (6) Organic salt containing Zr and Ca. Such ceramic composition can satisfy the X8R characteristic of the EIA standard.
In U.S. Pat. No. 7,262,146, another ceramic composition is disclosed. 100 moles of BaTiO3 is used as the main component and the subcomponents include (1) 0.1 to 3.0 moles of the oxides of Mg, Ca, Ba and Sr (2) 2.0 to 10.0 moles of a sintering auxiliary reagent (3) 0.01 to 0.5 mole of the oxides of W, V and Mo (4) 0.5 to 7.0 moles of R1 (Sc, Er, Tm, Yb and Lu) (5) 0 to 5.0 moles of CaZrO3 (6) 0 to 9.0 moles of R2 (Y, Dy, Ho, Tb, Gd and Eu) (the total quantity of R1 and R2 is less than 13 moles) (7) 0 to 0.5 mole of MnO (8) 0 to 4 moles of the oxides of Al, Gr, Ga and Ge. Such ceramic composition can satisfy the X8R characteristic of the EIA standard.
In U.S. Pat. No. 7,297,403, another ceramic composition is disclosed. 100 moles of BaTiO3 is used as the main component and the subcomponents include (1) 0.1 to 3.0 moles of MgO, CaO, BaO and SrO (2) 2.0 to 10.0 moles of SiO2 (3) 0.01 to 0.5 mole of V2O5, MoO3 and WO3 (4) 0.5 to 0.7 mole of the oxides of Sc, Er, Tm, Yb and Lu (5) 0 to 5.0 moles of CaZrO3 (6) 0 to 9.0 moles of Y, Dy, Ho, Tb, Gd and Eu (rare earth elements) (7) 0 to 0.5 mole of MnO. Such ceramic composition can satisfy the X8R characteristic of the EIA standard.
In U.S. Pat. No. 7,381,464, two ceramic compositions are disclosed. One of the two ceramic compositions comprises 100 moles of BaTiO3 is used as the main component and the subcomponents include (1) 2 to 10 moles of the oxides of Mg, Ca, Ba and Sr (2) 0.01 to 0.5 mole of the oxides of V, Mo and W (3) 0.5 to 7 moles of the oxides of Sc, Er, Tm, Yb and Lu (4) 0 to 5.0 moles of CaZrO3 (5) 0 to 9.0 moles of Y, Dy, Ho, Tb and Eu (rare earth elements) (6) 0 to 0.5 mole of MnO. Such ceramic composition can satisfy the X8R characteristic of the EIA standard.
The other ceramic composition disclosed in U.S. Pat. No. 7,381,464 comprises 100 moles of BaTiO3 as used as the main component, and the subcomponents include (1) 0 to 0.1 mole of the oxides of Mg, Ca, Ba and Sr (2) 1 to 7.0 moles of Y, Dy, Tm, Ho and Eu (rare earth elements) (3) 2.0 to 10.0 moles of MxSiO3 (where M includes Ba, Ca, Sr, Li and B) (4) 0 to 0.5 mole of MnO (5) 0.01 to 0.5 mole of the oxides of V, Mo and W (6) 0 to 5.0 moles of CaZrO3. Such ceramic composition can satisfy the X8R characteristic of the EIA standard. In U.S. Pat. No. 7,396,791, another ceramic composition is disclosed. 100 moles of Bal-xCaxZrl-yTiyO3 (where 0<x<0.15 and 0<y<1.0) is used as the main component and the subcomponents include (1) 0.01 to 0.2 mole of the oxides of V, Mo and W (2) 1.0 to 10.0 moles of the oxides of Mg, Ca, Ba and Sr (3) 0.1 to 5 moles of the oxides of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu (4) 1 to 10 moles of SiO2. Such ceramic composition can satisfy the X8R characteristic of the ETA standard.
From the above, we can see that the compositions of the prior art have many disadvantages and need to be improved.
To eliminate the disadvantages of the compositions of the prior art, the inventor has put in a lot of effort in the subject and has successfully come up with the dielectric ceramic composition of the present invention.